Injection molding machines, die casting machines, and presses generally operate on an automated basis to sequentially mold large quantities of substantially identical parts with relatively little attention required by the operator. Injection molding machines in particular are in extremely widespread use for manufacturing a wide range of articles, including toys, household items, machine components, engine components, aircraft parts, marine parts, and spacecraft components, just to name a few of the many areas in which injection molded items are used. Indeed, a substantial portion of any and all items manufactured from thermosetting or thermoplastic polymers are made using injection molding techniques.
A typical injection molding machine includes a stationary platen and a moveable platen supported upon a frame structure. The stationary platen is fixed in place on the frame structure, and the moveable platen is slideable along the frame structure to allow the moveable platen to move toward and away from stationary platen in a rectilinear fashion. To help guide and support the moveable platen as it moves along the frame structure, the moveable platen is slideably supported upon tie bars, usually four in number, which are rigidly connected to stationary platen at one end and coupled to other componentry of the injection molding machine at their other end.
In a typical injection molding operation, a pair of complementary mold elements, or "mold halves", are provided which define a mold cavity when the mold elements are clamped together. The mold elements are mounted to the moveable and stationary platens, respectively, in a manner such that relative movement of the moveable platen towards the stationary platen causes the mold elements to be registrably clamped together, thus closing the mold cavity. Sufficient clamping force is usually applied to the mold elements so that molten molding material does not seep from the interface between the mold elements during the injection step in which molten material is injected into the mold cavity under pressure. After injection, the molten material is allowed and/or caused to solidify in the mold cavity to form a molded part. The moveable platen and its corresponding mold element are then driven away from the stationary platen, thus opening the mold cavity. The part is then ejected, and the cycle may be repeated.
One problem that continues to be associated with injection molding machines, and platens in particular, concerns the deformation of one or both platens that tends to occur during molding operations. During molding operations, substantial force is generated against the center region of each mold mounting face of the platens, and additional forces are generated against the backsides of each platen at the regions proximal to the locations at which the tie bars operationally engage each platen. Generally, such forces tend to cause the mold mounting faces of each platen to concavely deform. Such deformation undesirably causes a gap to form between the mold elements. This allows molten material injected into the mold cavity to leak from the gap, resulting in flash and/or other defects in the molded part. Even robust, heavy, block-shaped platens previously known in the art are subject to this kind of deformation problem.
Platens could be made extremely thick to avoid the deformation problem. However, this approach results in heavy platens and large-sized machines adapted to handle such heavy platens. This is not ideal, though, because it is generally desirable for platens to be as light and small as possible for speed and fast cycle times.
There exists, therefore, a need for a practical way in which complementary mold elements can be mounted to cooperating platens and then forcefully clamped together without causing deformation of the mold mounting face of either the moveable and/or stationary platens during molding operations.